This is actually E2M1. The original Butt.wad is available as part of Academy.wad, which is number 2509 in the archive. That level is a decent-looking deathmatch arena for the period, and you would be better off downloading it instead of this level, which is a very poor modification. It's smaller, it has fewer monsters, and there are several bugs and missing textures. Like its predecessory it is a deathmatch level, as there are only eight, weak, monsters.

I tell a lie. The Butt.wad in Academy.wad is just a sound replacement with noises from Beavis and Butthead (remember them?). There is a sequel to the original Butt.wad as number 557 in the archive, however.